Mechanical Properties and Microstructure of DMLS Ti6Al4V Alloy Dedicated to Biomedical Applications

Abstract

The aim of this work was to investigate the microstructure and mechanical properties of samples produced by direct metal laser sintering (DMLS) with varied laser beam speed before and after heat treatment. Optical analysis of as-built samples revealed microstructure built of martensite needles and columnar grains, growing epitaxially towards the built direction. External and internal pores, un-melted or semi-melted powder particles and inclusions in the examined samples were also observed. The strength and Young’s modulus of the DMLS samples before heat treatment was higher than for cast and forged samples; however, the elongation at break for vertical and horizontal orientation was lower than required for biomedical implants. After heat treatment, the hardness of the samples decreased, which is associated with the disappearance of boundary effect and martensite decomposition to lamellar mixture of α and β, and the anisotropic behaviour of the material also disappears. Ultimate tensile strength (UTS) and yield strength(YS) also decreased, while elongation increased. Tensile properties were sensitive to the build orientation, which indicates that DMLS generates anisotropy of material as a result of layered production and elongated β prior grains. It was noticed that inappropriate selection of parameters did not allow properties corresponding to the standards to be obtained due to the high porosity and defects of the microstructure caused by insufficient energy density.

Effect of Industrial Heat Treatment and Barrel Finishing on the Mechanical Performance of Ti6Al4V Processed by Selective Laser Melting

“…Indeed, the tests along different orientations were also intended to provide a verification of a substantial isotropy of the alloy, coherently with what is reported by the EOS Ti6Al4V datasheet [31], in which very similar yield stresses (945 and 965 MPa) and ultimate tensile strengths (1055 and 1075 MPa) are declared for the horizontal and vertical building directions, with the percentage differences falling below 2%. Analogous properties were also found by other authors [32][33][34][35], who used recent EOS SLM machines, as the one of this research. In these studies, the differences in terms of ultimate strength between the different orientations were within 4%.…”

The Effect of Position of Materials on a Build Platform on the Hardness, Roughness, and Corrosion Resistance of Ti6Al4V Produced by DMLS Technology

“…Longhitano [37] reports a lower roughness for as-built samples made under the same conditions as in our research, but he turned the sample by 30 • for each roughness measurement, eliminating the influence of the building direction, and stated lower final values than the authors of this article. The best match of results was obtained in [38], where Ra on the side wall of as-build samples produced by the same technology varied from 9 to 21 µm, according to scanning speed.…”

Electrochemical Evaluation of the Compact and Nanotubular Oxide Layer Destruction under Ex Vivo Ti6Al4V ELI Transpedicular Screw Implantation

“…This phenomenon was not observed in previous attempts [19,38] due to lower thickness of the nanotubular layer. This is favorable due to the osseointegration process because the surface roughness of nanotubular Ti6Al4V ELI are able to slightly increase after implantation [1].…”

“…The Ti6Al4V ELI (Grade 23) alloy is the most commonly used biomaterial for dental and orthopedic implants, and its advantages include good mechanical properties, machinability, biocompatibility, and excellent fatigue resistance [1]. However, the major concern of using this alloy in clinics is the presence of infiltrated aluminum and vanadium ions in its chemistry, which can potentially increase the expressions of pro-inflammatory factors and cause osteolysis, exhibiting a toxic effect in the body.…”